Process for producing crystalline spray dried material



Jan. 31, 1961 J. P. TERRETT ET L 2,970,057

PROCESS FOR PRODUCING CRYSTALLINE SPRAY DRIED MATERIAL Filed July 6, 1956 2 Sheets-Sheet 1 Ira/672275 Jo/z 72 P76172326,

Jan. 31, 196i .1- P. TERRETT ET AL PROCESS FOR PRODUCING CRYSTALLINE SPRAY DRIED MATERIAL Filed July 6, 1956 J h .F r

--/6 EJ p I 15 fig/ f [we/Z525 2,910,057 PROCESS FOR PRODUCING CRYSTALLINE SPRAY DRIED MATERIAL q John P.-Terrett, San Francisco,--JohnBishields, Sunnyvale, and Louis J. Nava,' Redwood' City,-Galif., assignors, by mesne assignments, to Dairy Foods Incorporated, "-Los Angeles, Calif., a corporation of California 'FiledJuly 6, 1956,"Ser. No. 596,232 17 Claims. .(Cl. 99-203) This invention-relates to a new and improved, process for producing crystalline spray dried materials and'more particularly to a method for supplying controllable amounts of seed crystals to concentratedlluid materials containing crystallizable substances which are to be converted substantially'to a crystalline form in 'the spray dried material. The seeding method herein disclosed ap plies to the spray drying ofconcentrated "fiuidmaterials jc'o'ntaining at leastone crystallizable substance which is to be rendered crystalline to a substantial degree during the drying operation. It is contemplated that the drying operation comprise one or' more stepsbut'thatthe initial step of the drying operation be accomplishedby spray.

drying.

An important feature of the present invention lies in "the fact'that the seeding step 'of the process'her'ein referred to'may'be carried out either before or after the concentrated"fiuid'material to be seeded has been concentrated to a degree sutticientto 'r'ender'said material 'saturated with'respect to the substance'or substances to be crystallized. 'The'advantages ofthisfeat'ure 'willbe apparent when it is considered thatthe usual method of "rendering crystalline crystallizable substances contained within a dehydratedmaterial involvesconc'en'tration of '-'the fluid material prior todrying to a high solidscontent at leastsuflicient to cause the crystallizable substance to exist in a supersaturated solution before the concentrated 'fiuidmaterial is seeded with an appropriate'quantity of the crystalline form of the-substance to be crystallized As stated above, we'have discovered that these disadvantages may be readily overcome by conducting the seedingoperation substantially simultaneously with the i atomization step 'ofspray'drying. 'In'practicing this invention; the concentrated "material may behafldld and processedunder conditions of concentration and't'empera- *"ture-well' outside the crystallization zone of the substance to be crystallized during the drying operation, thereby avoiding unnecessary losses of process timeas well as "special product handling equipment. A further advan- -tage*of the new process is that it is well suited to con tinuous plant operation.

Itisan object of the present invention to provide a fnewand improved 'processfor' producing crystalline spray dried materials.

United States Faten-t 'material to be spray dried substantially at the'tirne of 2,970,057 Patented Jan. 31, 1961 It is also an'object of the present invention to provide a new and improved method of introducing crystallization inducing seed points in concentrated fluid materials to be subjected to spray drying.

It is a further object to provide a seeding process which 'avoids'the necessity of developing a saturated'or supersaturated solution of the substance to'be crystallizedprior to spray drying.

It is an additional object to provide a method whereby seed'points'may 'be introduced into the-concentrated atomization.

It is another object to provide a method whereby seed points may be introduced into theconcentrated material to be spray dried just prior to atomization.

It is still another object to provide a process whereby materials bearing crystallizable substances may be seeded and spray dried to an essentially dry form containing controlled amounts of said crystallizable substances in crystalline form.

Although it will be apparent that the teachings of this invention may be advantageously applied to the dehydration of a wide variety of materials bearing crystallizable substances, we have found the principles herein disclosed especially advantageous in the controlled crystallization of milk sugar in spray dried milk and milk products. The merits of dried'milk products containing substantial quantities of theirlactose' content in theformof alphalactose hydrate" crystals have been-described bySharp in U-.S.'Patent No. 2,728,678, datedDecember 27,1955,

and in the application of'Sharp-and"Kempf, SerialNo. 544,862, filed'Dec'ember' 22, 1955.

'We have shown apparatus suitable for carrying out our improved methods in the accompanying drawings,'in which-- I 'Figure'l is a "diagrammaticrepresentation of-a spray drying system utilizing one or'more-pr'essure spray atomizers-=which serve to introducethe concentrated material -'-to bedried into a 'dryingch'arnber;

Figure 2 is a diagrammatic showing of a secondcom mon type 'of'spray drying apparatus in which the concentrated material to bespray dried may 'be atomized into a drying chamber by means of a centrifugal atomizer; Figure 3 is-a showing of thespray noz'zlearea shown 'infFigure 1 on an enlarged: scale; I

Figure 4 is= a showing," on anenla'r'ged scale, 'of the "apparatus used to feedseed matriaI direct-ly-iiito' the rotary atomizer of Figure 2; and

Figure 5- is a view, with certain parts omitte'd,"of 'the construction of Figure4 as seenfrom the right.

Referring to Figure 1, in-one method at carrying out our improved process, a suitable concentrated-material such'as milk concentrate is fed through feed line 4 into the pressure spray nozzle 1 by-means of high pressure feed pump 3. Simultaneously, aseed slurry is pumped by means of a high pressure" pump 6"-from' the'slurry surge tank 5 through the slurry feed line Tarid-mixing T 8, shown in Figure 3, into the milk concentrate as it enters the atomizing nozzle 1. Drying is accomplished by. means of drying airfed into-the drying chamber 2 through heater 9*and duct 10, and removed from the desiccator through fan .11. The powdered productis removed from the dryingchamb'erZZ by the drag' mecha- "-nis'm 12 which discharges into the'secondary' 'drier and cooler -13 after which the product iisgusually passed through a screening device 14 which discharges the prodnot into the containerlS.

A typical apparatus in which a rotary atomizer isemployed for carrying out'our process-is: shown in Figure 2 in which concentrated product to be dried "is :pumped to the rotary'atomizer'17 throughthe'product feedline 18'by' means ofthe feed pump" 16. In this-instance the seed material in either a slurry or powdered form is fed from the feed tank 19 through feeders 20 into the rotary atomizer 17 so that the concentrated product to be spray dried is combined with the crystallization inducing seed material substantially simultaneously with atomization. Drying air, provided in a manner similar to that shown in Figure 1, is introduced into the conical drying chamber 21 through the orifice 22 of the drier which is supplied by ductwork 23 and through tangential inlets shown at 24 and 25. The drying air is separated from the product by cyclone 27 and discharged therefrom through duct 26. The powdered product produced by this process passes from the drying chamber 21 through duct 28 and is discharged from collecting cyclone 27 into a screw mechanism 29 which in turn delivers the product into a secondary drier and cooler 38 before being screened at 31 and barreled at 32.

In Figures 4 and S, the rotary atomizer 17 is shown as driven by shaft 35 rotated by power supplied to pulley 37. The housing 39 encloses any well known type of water distribution system which serves to cool the bearings during operation. The details of the atomizer itself form no part of the present invention. The concentrate as a powder or as a slurry will be fed to the atomizer 17 through pipes 20 and the concentrate is fed through pipes 18. In the specific construction shown, each is fed through two pipes spaced 180 with the feeds alternated and spaced 90.

The particular manner in which either of the above described drying systems is operated will depend to a considerable degree upon the rate of crystallization desired in the process and will depend further upon the physical characteristics desired of the powered product. Usually, however, it is necessary to depart somewhat from conventional spray drying conditions in order that a significant degree of crystallization be brought about during the drying operation. In the case of milk products, appropriate drying conditions for the crystallization of substantial quantities of alpha-lactose hydrate have been described by Sharp in US. Patent No. 2,728,678, and by Sharp and Kempf in their application, Serial No. 544,862.

Essentially, the development of substantial quantities of alpha-lactose hydrate crystals in powdered milk prod ucts commonly involves the seeding of the concentrated milk product which has been concentrated to such a degree as to render it supersaturated with respect to alpha-lactose hydrate after which the concentrate is held for a sufiicient period of time to permit the development of relatively large quantity of crystals. This step is carried out before the spray drying operation which is preferably at somewhat lower than conventional desiccator temperatures so as to produce, as a result of spray drying, a powdered product having a moisture content of from approximately 8 to approximately 20 percent. Typically, the drying air fed to the drier may have a temperature of the order of from approximately 240 to approximately 350 F. and an air outlet temperature ranging from about 115 to about 160 F. depending upon a host of factors, chief among which are the degree of seeding and the physical characteristics desired of the finished product. Finish drying in a secondary drying system such as that shown in Figures 1 and 2, to a moisture content usually in the order of from 2 to percentserves to complete the process.

Although such processes as have been described for the crystallization of lactose in dried milk products operate effectively as to purpose, the degree of seeding is frequently critical and difficult to control by methods previously employed. We have found that the introduc- 70 tion of lactose seed crystals into the concentrate substantially simultaneously with spray drying to be an extremely efiicient means of imparting the necessary seed points to the product during spray drying. In most instances we have observed that less than 1 percent of seed 75 a consi r crystallilatitm of the material based upon the weight of the concentrate is effective in promoting the required amount of crystallization. However, when expressed on a weight basis, it is important to recognize that the quantity of seed material employed will depend to a considerable degree upon the size of the individual crystals added. In actual practice we prefer to use from approximately 0.1 to 1 percent of lactose crystals having a Tyler screen mesh size such as to pass through a 325 mesh screen. It will be apparent that the use of a coarser seed material will require higher seed levels to obtain equivalent performance to more finely divided seed material.

As has been stated above, one of the important advantages of the present invention lies in the fact that our seeding method is conveniently operable whether the substance to be crystallized exists in a condition of undersaturation, saturation, or supersaturation at the time of seeding. In other words, we have discovered that the operability of the present invention is not dependent upon a condition of saturation or supersaturation with respect to the substance to be crystallized provided the residence time of the seed within the fluid into which it is introduced is sufficiently short to avoid destruction of the crystallization inducing properties of the seed before a condition of saturation is reached as a result of subsequent dehydration. Apparently these conditions are satisfied to a high degree in spray drying due to the extremely rapid drying which the atomized product undergoes immediately upon being discharged from the atomizer.

The exact reason for the high degree of seeding 'effi- I ciency experienced in using the process of the present invention remains unknown to us. Theoretically, when a substantial degree of crystallization is sought, it is desirable to impart at least one seed crystal to each droplet formed of the material being atomized in the process of spray drying. Notwithstanding this fact we have consistently observed that efiicient seeding can be obtained by our seeding methods when the number of seed points supplied to the atomizer is substantially less than the theoretical requirement of one seed nucleus per spray droplet formed. By way of illustration, we have noted repeatedly that seed concentrations to the atomizer productive of only one seed crystal for approximately every ten or more spray droplets is effective in inducing substantially complete crystallization of the lactose content of milk powders produced in accordance with the methods referred to above.

Although an entirely satisfactory explanation for the observed degree of seeding efficiency is not readily apparent, it is conceivable that the effectiveness is due in substantial part to the high degree of agitation and mixing to which the mixture is subjected at the time of atomization which may occasion an extraordinarily high incidence of contact of a limited number of seed crystals with a relatively large mass of the concentrate being spray dried. That an unusually high incidence of contact between seed nuclei and the concentrated product being dried is possible is supported at least in part by the fact that crystalline seed material such as lactose possesses greater density than the concentrate seeded. Hence, under the influence of the forces developed in the seeded mass at the timeof atomization, the seed crystals may be caused to travel through the mass in such fashion as to contact relatively completely each portion thereof. Certainly the centrifugal forces developed in the rotary type atomizer are sufficient to bring about this migratory action of the seed crystals and although the centrifugal forces developed in the conventional spray nozzle are doubtless of a lesser magnitude it is conceivable that they may be of considerable importance to the end result.

In the practice of the present invention, it is contemplated that a wide variety of seed materials may be used. For example, in those systems in which adulteration is not crystallizable sub srance may be induced by foreign or inert materials as well as by crystalline forms of the substance to'be' crystallized. In the-case-of foodstuffs such asr'iiilk'arid'rnilk pro'duc'tsfit is usuallyprefe'rable to'employ'as seed a crystalline form of 'thesubsta'nce to be crystallized in order that adulteration be avoided.

-'With further reference to'thecrystalliz'a'tion of lactose pr milk andmilk products "during the process ofspray dryingfla' -v'ariety'of different forms 'of seed material such as powered ciifs'talliiie" lactose, powderedhrystallinebetalactose, powdered crystalline alpha-lactose hydrate, powdered crystalline" alpha-lactose anhyd'ride, powdered milk floutthe present-invention-are*presented for' 'purposes of illustration of-t-he method and not by way of limitation.

Fluid whole milk was concentrated to provide 5,000 pounds of concentrate testing 46 percent total solids. This material was spray dried using a rotary atomizer and spray drying equipment similar to that shown in Figure 2. The drying operation was carried out by preheating the concentrate to a temperature of 120 F. as it was fed to the drier at a rate of 5,000 pounds per hour while simultaneously feeding powdered crystalline alphalactose into the rotary atomizer at a rate of 12.5 pounds per hour. The powdered crystalline alpha-lactose was combined with the concentrated milk product within the rotary atomizer 17 by means of apparatus similar to that illustrated in Figures 4 and 5 in which the milk concentrate was fed into the atomizer 17 by means of concentrate feeders 18 while the seed lactose was introduced into the atomizer from the supply vessel 19 through feeders 20. The resulting mixture was immediately sprayed from the periphery of the rotary atomizer 17 and dried to a moisture content of 12 percent after which the powdered material passed into the collecting cyclone 27, as shown in Figure 2, and was discharged therefrom into the screw conveyor 29 from which it was passed into the final drying unit 30 prior to screening at 31 and packaging at 32. The resulting product had a moisture content of 2 percent and the lactose content was found to be substantially in the crystalline form.

Example 2 3,000 gallons of fluid skim milk was evaporated in the conventional manner to a total solids content of 44 percent. The resulting 5,300 pounds of concentrated skim milk was dried using a pressure spray, box-type drier similar in principle and function to the spray drying system illustrated in Figure 1 to which reference is made in the following description.

The concentrated skim milk was heated to a temperature of 125 F. and fed to the drier 2 at a rate of 4,100 pounds per hour by means of high pressure feed pump 3. Immediately prior to entering the atomizing nozzle 1 the concentrate was mixed with a previously prepared seed slurry held in surge tank 5 and fed into the product feed line 4 through slurry feed line 7 and mixing T 8 by means of high pressure pump 6 at a rate of 20 gallons per hour.

In this instance, the seed slurry was prepared by adding 325 mesh alpha-lactose hydrate crystalline seed material, at a rate of 1 pound of seed material per gallon of concentrate, to 32 percent total solids skim milk concentrate tempered to 50 F.

The drier was operated at an inlet air temperature of 320 F. and an outlet air temperature of 132 P. which conditions served to reduce the moisture content of the spray dried product to 15 percent as it was discharged from the desiccator 2. The product was then moved by means of the drag mechanism 12 into the secondary drier 13 where the moisture content was lowered to 3.5. pcr= "centbefore screening at'1'4 andpackagingat 15.

=Example 3 Fluid skim milk was concentrated to provi'de "5,000

" pounds or skim milk concentrate testing 44- percent total solids. This concentrate was seeded-en's spray dried-tinder substantially identical conditions to" those described in Example 1 with the exception tliatcrystalline alphalac'to'se aiihydride was ried as tlie-"seeding -rnaterial' and supplied to the ceatrirugar atomizer tita rate ef5-.2 .=poun'ds per hour.

'EJtiz'iitPle "4 Fluid skim was concentrated in the conventional-mam ner to a total solids content of'45 percent. 4,800 pounds of this concentrate was spray dried under conditions s ubs'tantiany identical to those employed in Exar-np l l'with the exception that the seed material was ki m'ilkpow- "'derfthe lactose eofitene of' which had tieen' previously crystallized. In this instance the skim milk powder hearing crystalline lactose was added to the concentrate to be dried within the centrifugal atomizer at a rate of 60 pounds per hour.

The product of all of these examples comprised a free flowing non-caking powder having the desirable characteristics of hydnate powder. In general, in carrying out our processes on the order of approximately 50 percent of the lactose is present in the product in crystalline form, although due to variations in the materials used and in details of the apparatus used this percentage may vary over a rather broad range of from 30 percent to 80 percent of the lactose in the crystalline alpha-lactose hydrate form.

What we claim is:

1. A process for producing crystalline spray dried material by a procedure which employs the step of adding seed material to fluid material containing at least one crystallizable substance which is to be rendered crystalline during the process of spray drying, which comprises concentrating said fluid material, thereafter simultaneously introducing said concentrated fluid material and said seed material into an atomizer, atomizing the seeded concentrated fluid material into a drying atmosphere, drying in said atmosphere the resulting atomized particles of said material to a state of at least saturation with re spect to said crystallizable substance to be rendered crystalline, and thereafter further drying said spray dried material to a moisture content productive of the desired keeping quality of the final dehydrated product.

2. A process for producing spray dried milk product which has a substantial portion of its lactose in crystalline form which comprises concentrating fiuid milk product, thereafter simultaneously introducing said concentrated milk product and seed lactose into an atomizer, atomizing said seeded milk product into a drying atmosphere, dry: ing in said atmosphere the resulting atomized particles of said milk product to a state of at least saturation with respect to said lactose, and thereafter further drying said spray dried milk product to a moisture content productive of the desired keeping quality of the final dehydrated milk product.

3. The method of claim 1 in which the seed material is in a finely divided dry from.

4. The method of claim 1 in which the seed material is added to the concentrated fluid material in the form of a slurry.

5. The method of claim 1 in which the fluid material is concentrated prior to spray drying to a degree below a condition of saturation with respect to the crystallizable substance to be crystallized.

6. The method of claim 1 in which the fluid material is concentrated prior to spray drying to the degree of at least saturation with respect to the crystallizable substance to be crystallized.

7. The method of claim 2 in which the concentrated.

milk concentrated to a degree below a condition of saturation with respect to the lactose content of said concentrated milk product.

8. The method of claim 2 in which the concentrated milk product is concentrated to a degree substantially above that at which saturation occurs with respect to the lactose content thereof.

9. The method of claim 2 in which the concentrated.

concentrated milk product.

13. The method of claim 2 in which the crystalline lactose seed material in the form of a slurry is added to the concentrated milk product.

14. The method of claim 2 in which the spray drying process is accomplished using a pressure spray type atomizer.

15. The method of claim 2 in which the spray drying process is accomplished using a centrifugal type atomizer.

16. The method of claim 2 in which the seed material is a milk product in powder form containing lactose crystals.

17. The method of claim 2 in which the seed material is a milk product containing lactose crystals.

References Cited in the file of this patent UNITED STATES PATENTS 891,366 Hatmaker June 23, 1908 2,088,606 Peebles et al Aug. 3, 1937 2,728,678 Sharp Dec. 27, 1955 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,970,057 January 31, 1961 John P, Terrett et a1 It is hereby certified'that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 6, line for ued" read used same column 6, line 63, and column 7, line 16, for "from", each occurrence,

reed form column 8, line 16, list of references cited, :zcr "891,366" read 891,336

Signed and sealed this 13th day of June 1961.

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. A PROCESS FOR PRODUCING CRYSTALLINE SPRAY DRIED MATERIAL BY A PROCEDURE WHICH EMPLOYS THE STEP OF ADDING SEED MATERIAL TO FLUID MATERIAL CONTACTING AT LEAST ONE CRYTALLIZABLE SUBSTANCE WHICH IS TO BE RENDERED CRYTALLINE DURING THE PROCESS OF SPRAY DRYING, WHICH COMPRISES CONCENTRATING SAID FLUID MATERIAL, THEREAFTER SIMULTANEOUSLY INTROUDUCING SAID CONCENTRATED FLUID MATERIAL AND SAID SEED MATERIAL INTO AN ATOMIZER, ATOMIZING THE SEEDED CONCENTRATED FLUID MATERIAL INTO A DRYING ATMOSPHERE, DRYING IN SAID ATMOSPHERE THE RESULTING ATOMIZED PARTICLES OF SAID MATERIAL TO A STATE OF AT LEAST SATURATION WITH RESPECT TO SAID CRYTALLIZABLE SUBSTANCE TO BE RENDERED CRYSTALLINE, AND THEREAFTER FURTHER DRYING SAID SPRAY DRIED MATERIAL TO A MOISTURE CONTENT PRODUCTIVE OF THE DESIRED KEEPING QUALITY OF THE FINAL DEHYDRATED PRODUCT. 